The present invention relates to computer printers and particularly to a device for mounting a paper tractor assembly on the printer frame.
In a computer printer, paper is pulled by means of a pair of paper tractors from a supply across a platen where characters are printed. The paper is conventionally a continuous, folded sheet having rows of spaced holes along its margins. Each paper tractor has a toothed sprocket wheel (or belt) that engages the spaced holes in the paper so that as the sprocket wheel is incrementally rotated, the paper is indexed, line by line, across the platen.
Each paper tractor is mounted on a circular support rod extending across the width of the platen and secured at each end to the sides of the printer frame. The paper tractors are slidably mounted on the support rod so that they can be moved from side to side to accommodate different widths of paper and different marginal spacings.
A square drive rod extends parallel to the support rod so that it can slidably engage a square hole in the sprocket wheel of each paper tractor and thus provides a mechanical drive means for any position of the paper tractors along the width of the platen. In conventional practice the drive rod is rounded at its ends in order to be journalled into the sides of the printer frame. Suitable drive gears are provided for the rotation of the drive rod.
Paper tractors in computer printers are items which have a high incidence of failure and are subject to frequent repair or replacement. As a result, it is important that they be easily removed and replaced without significant dismantling of the computer printer paper tractor assembly or the printer itself.
Furthermore, in terms of manufacturing the paper tractor assembly, it is undesirable to have to round off the square ends of the drive rod in order to accommodate those ends to a bearing mounted in the frame of the computer printer.